1. Field of the Invention
The present invention relates to a program exposure calculating apparatus. More specifically, the present invention relates to a program exposure calculating apparatus comprising a plurality of program lines employed in a single lens reflex camera.
2. Description of the Prior Art
Program exposure calculating apparatuses determining relation between an aperture value and exposure time for a prescribed exposure value on a program line have been widely used as the exposure calculating apparatuses for single lens reflex cameras. Provision of a plurality of program lines and the selection of program lines corresponding to information of focal length of a lens in such program exposure calculating devices have been proposed.
However, a program exposure calculating apparatus has not been proposed which is adapted to select a program line having steeper slope as the focal length becomes shorter. Generally, a lens having shorter focal length, that is, a wide-angle lens is used for taking a picture of a wide range as well as for taking a picture with great depth of field. Therefore, when a wide-angle lens is used, the aperture should be smaller. A lens having long focal length, that is, a telephoto lens is used for taking a picture of a remote object as well as to take a picture with the background vignetted by setting the depth of field small. Therefore, when a telephoto lens is used, the aperture should be larger.
Meanwhile, if the exposure time becomes longer than (l/f) second with the focal length of the photographing lens represented by f(mm), the picture is possibly blurred due to a camera shake.